1. Field of the Invention
This invention relates to a fuel filter for an engine and more particularly to a fuel filter for separating water from fuel contained therein and is most suitable to a marine engine.
2. Description of Related Art
At the present time, a large number of engines are used for marine application such as an outboard motor and a stem drive system. A fuel supply system is provided for supplying fuel to the engine. For example, a fuel tank is a first component of the fuel supply system for an engine of an outboard motor and it is located generally in a watercraft with which the outboard motor is associated. The other components of the fuel supply system, except a manually operable fuel pump, are placed on the engine that is accommodated in the outboard motor.
In the meantime, the fuel supply components for marine engines are situated under relatively rigorous conditions. Particularly, circumambient water can break into them unless any protection is given. The components on the engine are well protected against the water by a top cowling member and a bottom cowling member both surrounding the engine. However, the fuel tank is likely to be laid on a deck without any protection against the water invasion. Accordingly, water may intrude into the fuel supply system from the fuel tank. The water mingled with the fuel may not only exert undesirable influence to engine operation but also jeopardize engine life.
In order to prevent water from entering the engine (more specifically, its combustion chamber), the fuel supply system generally has a fuel filter therein to separate water from fuel in addition to removing foreign substances. Most of the fuel filters employ a vessel into which fuel containing water is induced. Water has the specific gravity greater than that of the fuel if it is gasoline or kerosene. Because of the differences in the respective specific gravity of the two liquids, the water is separated from the fuel and accumulates under the fuel layer, i.e., at the bottom of the vessel.
For example, an engine operating on a four stroke principle is one of such engines. Because lubricant is not mixed with the fuel in this four stroke engine, much less water may not be present in the fuel.
A direct cylinder injected engine is another one of such engines. This engine has a fuel injector for directly spraying fuel into a combustion chamber. The sprayed fuel is mixed with air charge induced through an air induction device into the combustion chamber for combustion. The air fuel ratio must be strictly controlled for good emissions in this engine. If, however, water is mingled to the fuel, the air fuel ratio will be apparently changed. Thus, the direct cylinder injected engine is not compatible with water mingled with fuel.
In the meantime, marine engines, particularly an outboard motor, easily generate much vibration. One of the reasons is that the outboard motor is arranged to be detachable from a hull of a watercraft and hence it cannot be very strictly fixed thereto. Due to the much vibration, conventionally, water in fuel is likely to be mixed up with the fuel and both of the water and the fuel are hardly separated from each other during the engine is running.
It is, therefore, a principal object of this invention is to provide a fuel filter that is rarely influenced by vibration in separation of water from fuel.
Also, an operator of an outboard motor must check regularly if water accumulates in the fuel filter. However, this check usually compels the operator to take an unnatural position because the operator should approach the fuel filter from the watercraft.
It is, therefore, another object to provide a fuel filter whereby accumulated water therein can be checked easily.
It is an idea to provide a water detection mechanism in a fuel filter and also a warning system at an appropriate location to indicate the water accumulation to the operator of the engine so that the operator may throw the accumulated water away as well as deposited foreign substances at proper timings. However, as described above, there is much vibration in the engine. Thus, the water detection mechanism must be arranged to work accurately even under the circumstances.
It is, therefore, a further object to provide a fuel filter wherein a water level is accurately sensed with a water detection mechanism even there is vibration in the engine.
Also, room or a space for the fuel filter is generally small in the engine if it is for an outboard motor. Because, as described above, cowling members are provided around it. Accordingly, the fuel filter should be formed as small as possible even a water detection mechanism is contained therein.
It is, therefore, a firther object to provide a compact fuel filter that can still contain a water detection mechanism.